[AnthonyMouse]

That's a bad argument. There are gasoline trucks with a GVWR of ~20,000 pounds and diesel cars that weigh less than a Honda Accord. If you actually wanted to do that then you'd instead do something like tax based on axle weight and miles traveled, e.g. by reading the odometer during inspections.

The better argument is that diesel is worse for air quality and then it's a pigouvian tax in proportion to how much you burn.

The realpolitik argument is that fewer people have diesel vehicles and democracy is two wolves and a sheep voting on what's for dinner. But taxing commercial trucks is also a pretty sneaky way of taxing ~everything while pretending to not, so it's also the principal/agent problem. Legislators want to spend money while pretending not to take it from you.

[cma]

> diesel cars that weigh less than a Honda Accord.

It is taxed less than gas in lots of Europe where that is more common. You also need to factor in mpg vs gas, where it is higher, so more road-wear pCO2 was part of the debate in Europe, even though it is longer carbon chain so worse co2 ratio per calorie, the engines are more efficient. Diesel is worse for local air, better for long term co2.

There are a mixture of factors and lobbying behind the differencs, road wear is one. Farm fuel with no road wear isn't taxed much at all in lots of places and is more often diesel.

[AnthonyMouse]

> It is taxed less than gas in lots of Europe where that is more common.

But then it's even worse at recovering the cost of road maintenance from heavy trucks.

> You also need to factor in mpg vs gas, where it is higher

Passat TDI (diesel), ~3500 pounds, ~45MPG. Toyota Camry Hybrid (gas), ~3500 pounds, ~50MPG.

In theory diesel hybrids would be even more efficient but diesel engines and hybrid transmissions both add up-front cost and further efficiency improvements have diminishing returns because reducing a $100 fuel cost by 30% isn't as much money as reducing a $70 fuel cost by 30%.

> There are a mixture of factors and lobbying behind the differencs, road wear is one.

Road wear is the irrelevant one in terms of fuel. Because of the fourth power law, essentially all road wear is from full-size buses and semi trucks. The contribution from passenger cars and even the likes of diesel pickup trucks rounds to zero. Meanwhile the largest vehicles use a minority of the fuel because there are several times more passenger cars than semi trucks.